The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
A typical automatic transmission includes a hydraulic control system that, among other functions, is employed to actuate a plurality of torque transmitting devices and to provide lubrication and cooling to the components of the transmission. The conventional hydraulic control system typically includes a main pump that provides a pressurized fluid, such as automatic transmission oil, to a plurality of valves and solenoids within a valve body. The main pump is driven by the engine of the motor vehicle. The valves and solenoids are operable to direct the pressurized hydraulic fluid through a hydraulic fluid circuit to the components of the transmission. For example the pressurized hydraulic fluid delivered to the torque transmitting devices is used to engage or disengage the devices in order to obtain different gear ratios.
In order to increase the fuel economy of motor vehicles, it is desirable to stop the engine during certain circumstances, such as when stopped at a red light or idling. However, during this automatic stop, the pump is no longer driven by the engine. Accordingly, hydraulic fluid pressure within the hydraulic control system drops. This leads to clutches and/or brakes within the transmission to be fully disengaged. As the engine restarts, these clutches and/or brakes may take time to reengage fully, thereby producing slippage and delay between engagement of the accelerator pedal or release of the brake and the movement of the motor vehicle. One solution is to include an accumulator to pressurize the transmission at the start of an auto-start event. However in certain configurations the accumulator and the fluid stored within the accumulator are exposed to ambient temperature conditions and therefore may not be at the same temperature as the transmission during an engine start event after prolonged exposure. Therefore, there is a need in the art for a system and method for controlling the discharge of an accumulator that preserves the ability to perform engine stop-start events without affecting transmission operating performance.